Firearms that are capable of automatic or semi-automatic operation, such as the M-16 rifle, are replete and extremely well known. Accuracy using such firearms is not successful unless the firearm is fired in short bursts due to the recoil of successive rounds causing the barrel of the firearm to climb upwardly and to the right, for the right handed shooter. The M-16 rifle, for example, fires at a cyclic rate of approximately 750 rounds per minute (RPM) wherein this rate, as combined with the impulse produced by a 5.56 mm cartridge makes it difficult for the shooter of such a firearm to consistently produce a controlled pattern of shots.
There have been numerous attempts that have been made to reduce the cyclic rate of fire of automatic and semi-automatic firearms, using a buffer assembly, wherein the recoil force is stored by the action or operating spring of the firearm and the bolt is returned from the recoil position to the battery position. For example, U.S. Pat. No. 3,977,296 describes a typical hydraulic buffer assembly used for decreasing the cyclic firing rate. According to the design of the '296 buffer assembly the bolt carrier, bolt and the buffer are each accelerated rearward from the battery position when the automatic firearm is fired. Each of the bolt, bolt carrier and the buffer are moved in unison toward the recoil position against the action or operating spring of the firearm. An elastomeric bumper provided on the end of the buffer contacts the end wall of the receiver extension. At this point, the buffer compresses and forces hydraulic fluid contained within the buffer through an orifice provided in a cylinder, thereby creating a resisting force. This resisting force decelerates the bolt as well as the bolt carrier, thus extending the recoil period. Furthermore and during counter-recoil (e.g., return of the bolt/bolt carrier assembly and buffer to the firing position), there is less rebound energy from the end of the recoil stroke such that the buffer/bolt are returned at a slower rate, which further delays the return of each of the assemblies back to the battery position. This delay thereby results in a slower firing rate of the firearm. Upon return to the battery position, the buffer also absorbs some of the kinetic energy of the bolt and the bolt carrier as they stop on the breech end of the barrel, such that these elements do not “bounce” off the breech end of the barrel.
There are a number of problems noted with regard to the above-described buffer design. First, the '296 buffer relies upon the use of dynamic seals. Dynamic seals, however, are more prone to leakage than static seals. The design of the above described '296 buffer includes a pair of dynamic seals, each of which create a potential leakage path. Hydraulic fluid loss can result in degraded performance. The internal spring of the '296 buffer continually acts upon the damping fluid, which in turn acts to hydraulically extend the piston rod. If the buffer unit leaks enough fluid, the piston will be compressed by the action spring thus reducing or eliminating the stroke in the buffer. The buffer would then merely act as a single mass only within the gun recoil system—which may only marginally reduce the firing rate and perhaps no longer reduce the condition known colloquially as “bolt bounce” from occurring. Bolt bounce has the potential for stopping the automatic firing sequence before the operator has the intention to do so.
In addition, the seals that are used in the '296 design are simple O-rings, each sealing dynamically upon an internal diameter bore, upon which can be difficult to obtain a smooth, hard, defect-free surface finish. This form of seal is prone to “weeping”, and is also more prone to rolling or twisting within its groove—the latter also leading to potential leakage. The '296 buffer design further relies upon a spring—loaded accumulator to provide a force that is sufficiently high enough to exceed the preload of the action spring of the firearm and thereby maintain the piston rod in the extended position. This form of accumulator provides a positive internal pressure within the buffer at all times. This pressure further acts to force the hydraulic fluid out of the buffer at all times.
Furthermore, the above-described '296 hydraulic buffer has four (4) separate stroke lengths that require size considerations in the placement of same in the firearm and making application of this design difficult in guns having shorter stocks. A buffer, such as the above-described '296 design, further includes the elastomeric plug or bumper which holds the spring in place, which in turn loads the sliding seal separator. If this plug or bumper were to loosen even partially, the function of the buffer would degrade.